1. Field of the Disclosure
The present disclosure relates to a digital angular velocity detection device that uses a micro electro mechanical system (MEMS).
2. Description of the Related Art
A general digital angular velocity detection device such as a gyroscope measures rotational frequency with respect to a rotation direction of an object, and is usually used in the navigation devices in a ship or an aircraft. The gyroscope measures the angular velocity based on a principle that a Coriolis force is applied vertically to the rotation direction. Nowadays, as semiconductor technology is developed, the gyroscope has been produced using MEMS technology.
FIG. 1 explains the operation principle of a micro gyroscope using the general MEMS technology.
As shown in FIG. 1, the micro gyroscope is constituted by a vibratory mass 11, and a movable electrode 12 connected to the mass 11. This causes variations in the electrostatic capacitance with a fixed electrode 13 as a rotation force is applied to the mass 11 in a vertical direction to the vibration thereof. An elastic member 14 is connected between the movable electrode 12 and the fixed electrode 13. A housing 10 supports the fixed electrode 13.
If the rotation force is applied from the outside when the mass 11 vibrates, the Coriolis force is given in a vertical direction to the rotation force. When the Coriolis force is given in a direction “F”, a distance between the movable electrode 12 and the fixed electrode 13 decreases. This reduction in distance generates a variation of the electrostatic capacitance there between. The micro gyroscope measures variation of the angular velocity by converting the electrostatic capacitance variation to a voltage variation.
However, the above-structured micro gyroscope needs to keep the mass 11 vibrating continually for the measurement of the angular velocity variation. Therefore, if the rotation force is not applied from the outside, the vibration of the mass 11 itself can cause a measurement error. Further, in order to generate and measure the capacitance variations between the movable electrode 12 and the fixed electrode 13, the distance between the-movable electrode 12 and the fixed electrode 13 needs to be as short as possible. On the other hand, a contact area therebewteen should be large. Such a requirement complicates the structure of the three-dimensional electrode and the fixed electrode.
FIG. 2 shows a related art structure of the electrodes constituting the micro gyroscope of FIG. 1.
As shown in FIG. 2, in the conventional micro gyroscope, the distance between the movable electrode 12 and the fixed electrode 13 is very short to guarantee sufficient capacitance between them. Further, the movable electrode 12 and the fixed electrode 13 are disposed very high from a semiconductor substrate. The manufacturing process to make such a three-dimensional structure using semiconductor technology is very complex. Moreover, it is hard to keep the distances between the movable electrode 12 and the fixed electrode 13 regular.